The present invention relates to an electronic device with a keypad and an audio speaker, and more particularly, to an electronic device with a keypad and a planar electromagnetic transducer that is co-planar to the keypad.
FIG. 1 is a cross-sectional view of a cone-type speaker 10. The cone-type speaker 10 moves a cone 12 in response to an amplified, electrical audio signal to produce a sound wave. The cone 12 is attached at one end to a coil 14 and at an opposing end to a to an outer ring of a speaker support 16 with a flexible mounting 18. The coil 14 is mounted so that it can move freely inside of a magnetic field of a permanent magnet 20. An enclosure 22 is provided to minimize the impact of the mechanical frequency of vibration of the cone. Such cone-type speakers require a relatively large amount of space and, unless quite expensive, have a limited dynamic range.
An alternative to the dynamic speaker is the electrostatic loudspeaker. The electrostatic principle provides a more faithful rendition of sound due to the superior speed and control of its diaphragm. Instead of a cone and its many associated parts, the electrostatic speaker uses a thin sheet of polyester or plastic material stretched taught on a frame and spaced between two stator plates. The diaphragm is charged with a high static voltage and a signal from the amplifier is applied to the stator plates through a step-up transformer to raise the signal""s voltage. The changing voltage on the stators moves the diaphragm back and forth, which in turn pushes the air around the diaphragm and creates sound. Since the diaphragm is extremely light, it is also extremely fast and thus responds quickly and accurately to audio signals. This gives such flat speakers an extraordinarily xe2x80x9cclearxe2x80x9d sound.
Another alternative is the planar magnetic speaker, such as disclosed in U.S. Pat. No. 5,283,836 and U.S. Pat. No. 6,008,714. Planar-magnetic speakers use a membrane with a coil etched into it and located between two magnetic panels. They basically work the same way as electrostatic speakers, except that the alternating positive and negative current moves the membrane in a magnetic field rather than an electric field. Like electrostatic speakers, they produce high-frequency sound with extraordinary precision.
Most electronic devices today include a cone-type dynamic loudspeaker. However, as discussed above, such cone-type speakers, unless at the very high end, do not reproduce sound as well as flat panel speakers. Further, the speaker cone requires a relatively large amount of space. Since electronic devices are being used to play audio files, such as music stored in an MP3 file, it would be desirable to provide such electronic devices with a higher fidelity sound system.